Magnetic chemically peculiar stars with variable periods

Zdeněk Mikulášek (PřF MU Brno)

The majority of magnetic chemically peculiar (mCP) stars exhibit periodic light, magnetic, radio, and spectroscopic variations that can be adequately explained by the model of a rigidly rotating main-sequence star with persistent surface structures. Nevertheless, there are a few quite diverse mCP stars whose periods vary on timescales of decades while the shapes of their phase curves remain unchanged. Alternations in the rotational period variations, suspected in the case of CU Vir and V901 Ori, bring further new insight into this theoretically unexpected phenomenon. The possible causes of this mysterious behaviour will be also discussed. 
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